The present invention relates to a surface state monitoring method and apparatus for performing in-situ monitoring of surface states of semiconductor substrates by infrared spectroscopy at fabrication site of semiconductor devices.
Various requirements at fabrication sites of semiconductor devices require surface states of the semiconductor substrates being accurately grasped.
To give an example, in the field of semiconductor integrated circuits of memory devices, such as DRAM (Dynamic Random Access Memory), etc., and of logic devices, to form a gate insulation film having dielectric breakdown voltage of a required value, it is very important that surface states of a semiconductor substrate are administered. As a device has higher integration, the gate insulation film at the time of the fabrication of the device is made thinner, and the device has a design that the function for insulating an electric field (about 4xc3x97106 V/cm) of a MOS (Metal Oxide Semiconductor) FET (Field Effect Transistor) in operation has a small margin. Generally, a gate insulation film is formed by thermal oxidation. In forming a gate insulation film by thermal oxidation, in a case of surface contamination, as of metal contamination, chemical contamination, organic contamination or others is present, there is a risk that dielectric breakdown of the formed gate insulation film may be induced. It is known that organic contaminants stayed on the substrate surfaces after the gate insulation film has been formed results in insulation deterioration.
Plasma etching is widely used in steps of patterning device structures. In the plasma etching process, to set optimum plasma etching conditions and to detect the end point of the plasma etching, it is very effective to know adsorption states, chemical bonding states, structures and thicknesses of reaction layers, etc. of surface states of semiconductor wafers. The plasma etching process is determined by dynamic balance in adsorption, reaction and elimination processes between influxes of radical ions, etc. fed in gas phase and outfluxes from semiconductor wafer surfaces.
Recently, semiconductor devices have elements increasingly micronized, and are made increasingly three dimensional. This makes it difficult for cleaning solutions to intrude into micronized regions or steep steps or to be replaced there. In consideration of future further micronization, dry cleaning is noted. For example, to remove organic contaminants staying on semiconductor wafers reaction with ozone or oxygen excited by UV radiation is effective. Oxygen molecules are dissolved to oxygen atoms by light of a below 242 nm wavelength. The organic,contaminants are oxidized by the oxygen atoms and solved into H2O, O2, CO, CO2, etc. of high vapor pressures. Organic bonds, such as Cxe2x80x94C, Cxe2x80x94H, Cxe2x80x94O, etc. can be dissolved by UV radiation. Thus, knowing surface states of semiconductor wafers is very important also to control parameters for the dry cleaning, such as an optimum amount of radiation, wavelength, oxygen amount, etc.
Native oxide films formed on the surfaces of semiconductor wafers are not usable in devices because their thickness cannot be controlled. Accordingly, it is preferable that when a device is fabricated on a semiconductor wafer, native oxide film on the silicon substrate is removed, and silicon bonds on the surfaces are terminated with hydrogen to stabilize the surfaces of the semiconductor wafer. This is because hydrogen can be eliminated at a relatively low temperature of about 500xc2x0 C., and the termination with hydrogen relatively little affects the following processes. Most of silicon atoms on the surfaces of a semiconductor wafer subjected to UV ozone cleaning and hydrogen fluoride etching are terminated with hydrogen, and Sixe2x95x90H2 and Sixe2x80x94H are formed. Accordingly, if a state of the termination with hydrogen on semiconductor wafer surfaces, temperature dependency of the elimination of terminating hydrogen can be monitored, the semiconductor wafer surfaces at the start of semiconductor processing can be kept in a suitable state. Higher quality and higher yields can be expected.
Thus, it is very important to know a surface state of a semiconductor wafer in a fabrication process of a semiconductor device, and various monitoring methods and apparatuses have been proposed and locally practiced.
Means for monitoring a surface state of a semiconductor wafer by internal multiple reflection of infrared radiation is provided by, e.g., FT-IR (Fourier Transform-Infrared spectroscopy) apparatus of the special use marketed by Perkin-Elmer Co., U.S.A. For wider applications of the means Graseby Specac Limited, for example, markets various accessories.
In the conventional surface state monitoring method using this means, as exemplified in FIG. 12A, a substrate-to-be-monitored 102 is cut into, e.g., a 40 mmxc3x9710 mm strip, and infrared radiation emitted from an infrared radiation source 104 is passed through the substrate-to-be-monitored 102 to monitor states of the substrate surfaces. Otherwise, as exemplified in FIG. 12B, a substrate-to-be-monitored 102 has the end tapered, and infrared radiation is incident on the end surface of the substrate-to-be-monitored 102 to undergo multiple reflection inside the substrate, whereby a surface state of the substrate is monitored. Otherwise, as exemplified in FIG. 12C, infrared radiation is incident on a substrate-to-be-monitored via a prism 106 positioned above the substrate to undergo multiple reflection inside the substrate, whereby a surface state of the substrate is monitored.
The basic principle of monitoring a surface state of a substrate by applying infrared radiation to a substrate to cause the infrared radiation to undergo multiple reflection inside the substrate is that spectra of frequency components of evanescent waves oozing when light reflects on the substrate surfaces are resonance-absorbed when they agree with molecular vibrational frequencies of organic contaminants on the substrate surfaces are measured, whereby kinds and amounts of the organic contaminants can be determined. The basic principle also has a function that information of organic contaminants on substrate surfaces is gradually made more exact. A signal vs. noise ratio (S/N ratio) is also improved.
However, these monitoring methods needs cutting a substrate-to-be-monitored into strips, additionally machining a substrate-to-be-monitored, or disposing a prism above a substrate-to-be-monitored. These monitoring methods have not been usable in the in-situ monitoring at site of fabricating semiconductor devices.
Methods of monitoring organic contaminants on semiconductor substrates are known thermal desorption GC/MS (Gas Chromatography/Mass Spectroscopy), APIMS (Atmospheric Pressure Ionization Mass Spectroscopy), TDS (Thermal Desorption Spectroscopy), etc. However, these methods are not suitable to be used in in-situ monitoring at site of fabricating semiconductors for reasons that these methods cannot directly observe large wafers of, e.g., above 300 mm-diameters which are expected to be developed, and need vacuum ambient atmosphere, and have a low throughput, and other reasons.
As described above, the above-described conventional surface state monitoring methods are not usable in the in-situ monitoring at site of fabricating semiconductor devices because the monitoring by these method is destructive, or these methods are not suitable for monitoring large semiconductor wafers. Surface state monitoring methods and apparatuses which permit the in-situ monitoring of substrate surfaces at site of fabricating semiconductor devices, and permit large wafers to be monitored have been expected.
An object of the present invention is to provide a surface monitoring method and apparatus which enable, at the site of fabricating a semiconductor device, in-situ monitoring of surface states of a substrate-to-be-monitored by infrared radiation spectroscopy of internal multiple reflection.
The above-described object is achieved by a surface state monitoring apparatus comprising: an incidence optical system for introducing infrared radiation into a substrate-to-be-monitored; a detection optical system for detecting the infrared radiation undergoing multiple reflections inside the substrate-to-be-monitored and exiting from the substrate-to-be-monitored; a surface state monitoring means for monitoring a surface state of a surface of the substrate-to-be-monitored, based on infrared radiation detected by the detection optical system; a position detecting means for optically detecting a position of the wafer-to-be-monitored; and a control means for controlling a position and an angle at which the infrared radiation is incident on the substrate-to-be-monitored, corresponding to the position of the substrate-to-be-monitored detected by the position detecting means. A positional deflection of a substrate-to-be-monitored is detected, and a position and an angle of the infrared radiation source can be quickly adjusted, corresponding to the positional deflection of the substrate-to-be-monitored, whereby infrared radiation can be incident on the declined face of the substrate-to-be-monitored at a suitable position and at a suitable angle without affecting throughput of all steps as a whole, and an internal reflection angle can be controlled to be a suitable angle. Accordingly, a time of total reflections inside the substrate-to-be-monitored can be suitably controlled, and accordingly a surface state of the substrate-to-be-monitored can be monitored with higher accuracy.
In the above-described surface state monitoring apparatus, it is preferable that the control means controls the incidence optical system to thereby control a position and an angle at which infrared radiation is incident on the substrate-to-be-monitored.
In the above-described surface state monitoring apparatus, it is preferable that the control means controls the wafer mount to adjust a position of the substrate-to-be-monitored to thereby control a position and an angle at which infrared radiation is incident on the substrate-to-be-monitored.
In the above-described surface state monitoring apparatus, it is preferable that the position detecting means is disposed above a peripheral edge of the substrate-to-be-monitored, and includes a first radiation source for applying first radiation to a peripheral edge of the substrate-to-be-monitored and a first photo detector disposed opposed to the first radiation source across the peripheral edge of the substrate-to-be-monitored, for detecting the first radiation; and the position detecting means detects a position of the substrate-to-be-monitored in the horizontal direction, based on a position of radiation detected by the first photo detector.
In the above-described surface state monitoring apparatus, it is preferable that the position detecting means includes a second radiation source for applying second radiation to the peripheral edge of the substrate-to-be-monitored and a second photo detector for detecting the second radiation reflected by the peripheral edge; and the position detecting means detects a vertical position of the substrate-to-be-monitored, based on a position of radiation detected by the second photo detector.
In the above-described surface state monitoring apparatus, it is preferable that the first radiation source and/or the second radiation source applies the first radiation and/or the second radiation to a region containing a position for infrared radiation to be incident on the substrate-to-be-monitored.
In the above-described surface state monitoring apparatus, it is preferable that the first radiation source and/or the second radiation source traverses the first radiation and/or the second radiation around a position for infrared radiation to be incident on the substrate-to-be-monitored.
In the above-described surface state monitoring apparatus, it is preferable that the position detecting means optically detects a position of the substrate-to-be-monitored at a plurality of positions along the peripheral edge of the substrate-to-be-monitored.
In the above-described surface state monitoring apparatus, it is preferable that the first radiation and/or the second radiation is radiation having a wavelength different from the wavelengths of infrared radiation.
In the above-described surface state monitoring apparatus, it is preferable that the first photo detector and/or the second photo detector one-dimensionally or two-dimensionally detects a position of the substrate-to-be-monitored.
The above-described object is achieved by a surface state monitoring method for monitoring a surface state of a substrate-to-be-monitored by introducing infrared radiation into the substrate-to-be-monitored, detecting infrared radiation which has undergone multiple reflections inside the substrate-to-be-monitored and exited from the substrate-to-be-monitored, and analyzing the detected infrared radiation, a position of the substrate-to-be-monitored being optically detected, and a position and an angle at which infrared radiation is incident on the substrate-to-be-monitored being controlled corresponding to the detected position of the substrate-to-be-monitored.. A positional deflection of a substrate-to-be-monitored is detected, and a position and an angle of the infrared radiation source can be quickly adjusted, corresponding to the positional deflection of the substrate-to-be-monitored, whereby infrared radiation can be incident on the declined face of the substrate-to-be-monitored at a suitable position and at a suitable angle without affecting throughput of all steps as a whole, and an internal reflection angle can be controlled to be a suitable angle. Accordingly, a time of total reflections inside the substrate-to-be-monitored can be suitably controlled,. and accordingly a surface state of the substrate-to-be-monitored can be monitored with higher accuracy.
In the above-described surface state monitoring method, it is preferable that when the monitor is repeated a plurality of times with the substrate-to-be-monitored rotated to monitor a surface of the substrate-to-be-monitored substantially all over the surface, prior to the monitor for each time, a position of the substrate-to-be-monitored is optically detected, and a position and an angle of infrared radiation to be incident on the substrate-to-be-monitored are controlled corresponding to the detected position of the substrate-to-be-monitored.
As described above, according to the present invention, a positional deflection of a semiconductor wafer is detected, a position and an angle of the infrared radiation source can be quickly adjusted, corresponding to the positional deflection of the semiconductor wafer. Accordingly, according to the present invention, infrared radiation can be incident on the declined face of a semiconductor wafer at a suitable position and at a suitable angle, whereby an internal reflection angle can be suitably controlled. Accordingly, according to the present invention, a number of times of total reflections inside a semiconductor wafer can be suitably controlled, whereby surface states of the semiconductor wafer can be monitored with high accuracy.
Furthermore, according to the present invention, a position and an angle of the infrared radiation source can be quickly adjusted, corresponding to a positional deflection of a semiconductor wafer, whereby even in a case that a semiconductor wafer is rotated to monitor substantially all the surfaces thereof for organic contamination and chemical contamination, throughput of all steps as a whole are kept from being affected.